Given that the `Navigator` interface has been available since "forever", please see https://developer.mozilla.org/en-US/docs/Web/API/Navigator#browser_compatibility, it's somewhat difficult to see why these checks are actually necessary since the viewer is only intended for usage in browsers.
Looking at the history of the code, this functionality was originally placed in the general `src/shared/compatibility.js` file which could thus run in e.g. worker-threads and Node.js environments (where the `Navigator` interface isn't available).
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